Subspecialty Content: Regional, Obstetric, and Pediatric Considerations
Scope
Subspecialty items test whether you can adapt general principles to populations and techniques with altered physiology. Expect questions on local anesthetic pharmacology (pKa, protein binding, maximum doses, LAST management), neuraxial block levels and complications, obstetric physiology, and pediatric dosing and airway differences.
Regional anesthesia
Understand that pKa determines onset (closer to physiologic pH = more uncharged base = faster onset), while protein binding and lipophilicity drive duration and potency. Bupivacaine is highly cardiotoxic; ropivacaine is less so. For LAST, stop injection, secure the airway, and give 20% lipid emulsion per weight-based protocol. Know the differential for post-neuraxial hypotension and the signs of high spinal (bradycardia, apnea, hypotension).
Obstetrics
Pregnancy lowers MAC, reduces functional residual capacity, and increases oxygen consumption, so desaturation happens fast. Uterine blood flow lacks autoregulation; hypotension from a spinal drops perfusion directly. Left uterine displacement relieves aortocaval compression. Magnesium potentiates nondepolarizers.
Pediatrics
Infants have a relatively large head, small mandible, high glottis, and narrow cricoid; uncuffed tubes historically relied on the cricoid seal. Higher metabolic rate means faster desaturation and higher maintenance requirements. Weight-based dosing is the norm; verify concentrations before calculating volumes.
Trap patterns
Items often present a plausible but wrong maximum local anesthetic dose, confuse onset with duration determinants, or describe a pediatric airway as adult-like. Read whether the question asks for onset or duration before selecting a physicochemical property.
Rule of thumb
When a spinal causes hypotension, treat with vasopressor plus fluids and left uterine displacement, not Trendelenburg alone, because the gravid uterus still compresses the vena cava.